The present invention relates to a longwall mining machine of the type having a pivot arm which supports a cutter drum for rotation about an axis for working a mine face. In a mining machine of this type, the rotating cutter drum, which carries cutting bits on its outer periphery, is provided with spirals which assist in loading the mined material onto a face conveyor. In the past, such cutter drums have been provided with nozzles on the periphery of their spiral conveying flights for directing liquid onto the face area being mined to reduce the generation of dust. A typical drum assembly of this type is shown, for example, in copending application Ser. No. 240,506, filed Mar. 4, 1981 and assigned to the Assignee of the present application.
It has been found that as a longwall cutter drum advances along a mine face, the hardness of the material being mined is greater at the back of the cut than at the forward edge of the cut. The difference in hardness is a result of the high rock pressure which loads the back area of the cut to a greater degree than the forward edge. That is, the overhead rock pressure loosens the material being mined adjacent the forward edge of the cut so that the forward layers of the mineral being mined tend to break up. This condition does not exist at the back of the cut, with the result that the material is much harder in this region. Consequently, the cutting resistance presented to the cutting bits is much less at the edge of the face than at the back of the cut, for in the latter zone the cutting bits impinge on very hard mineral layers and are stressed severely. To facilitate smoother operation of the cutter drum and to reduce the stressing of the cutting bits working at the back of the cut, the number of bits carried by the drum at the end adjacent the back of the cut has been increased in prior art longwall machines. This, however, results in an intense evolution of dust which impairs the operation of the mining machine and makes dust control measures essential for its operation.